FC Study Guide 2026
Everything you need to pass the FC exam in one place: the exam format, every topic to study, real practice questions with explanations, flashcards, and full-length practice tests. Free, no sign-up needed.
📚 FC Topics to Study (22)
✍️ Sample FC Questions & Answers
1. What is the most common cause of premature heat exchanger failure in residential furnaces?
Chronically restricted airflow (dirty filters, closed registers) causes the heat exchanger to overheat repeatedly, leading to metal fatigue and cracking.
2. What minimum flame signal (microamps DC) is typically required for a furnace flame sensor to keep the gas valve open?
Most furnace control boards require at least 0.5–1.0 µA of DC flame signal to confirm ignition and hold the gas valve open.
3. Which terminal on a conventional thermostat wiring system carries the 24V common (return) signal?
The C (common) terminal completes the 24V circuit from the transformer secondary, providing a return path for connected devices.
4. What should a technician do if they encounter a safety violation during furnace installation?
Encountering a safety violation during furnace installation demands immediate action to prevent potential hazards. Continuing work could exacerbate the risk, while ignoring it is irresponsible and illegal. Stopping the installation and reporting the violation ensures proper rectification, protecting both the technician and the future occupants of the building.
5. What is the maximum length of single-wall metal connector pipe allowed between a Category I furnace and a Type B vent or masonry chimney?
Single-wall connector pipe is limited to 6 feet between the furnace outlet and the Type B vent or chimney connector per most codes.
6. What happens to a condensing furnace when the condensate drain is blocked?
Blocked condensate causes water to back up into the pressure switch tubing or inducer housing, tripping the pressure switch and shutting down the furnace.